The present invention relates to a magnetic tape cassettes, and more particularly to a compact magnetic tape cassette substantially equal in size to so-called Philips-type magnetic tape cassette.
Recently, cassette tape recorders have been remarkably reduced both in size and in weight. Accordingly, there has been a strong demand for the provision of a magnetic tape cassette which is small in size and which is suitable for signal recording and reproducing operations with high quality and high density and which has a long playing time.
Heretofore, in the use of a compact cassette with an audio device, analog signals have most commonly been employed for recording and reproducing operations. However, in the analog system, the density of signal recording is limited. On the other hand, it is well known in the art that a digital system such as a pulse code modulation system in which input signals are converted into pulses for recording and reproducing permits recording with a high density and without distortion by signal communication paths and the recording medium.
Recently, there has been developed a magnetic head with which multi-track signal recording and reproducing operations can be performed with a magnetic tape whose width is as small as that of the magnetic tape of a Philips cassette. As a result, it is possible to carry out multi-track signal recording and reproducing operations with a magnetic tape cassette which is as compact as the Philips-type cassette.
In the case where a multi-track signal recording operation is carried out with a compact cassette in a fixed magnetic head system, for instance, in a case of using thirty-six tracks for recording signals, the width of each track is of the order of 100 microns, which is extremely small when compared with the width of each track in a four-track signal recording operation using a standard Philips-type cassette. Accordingly, the effective area of the surface of the magnetic head which is brought into contact with each track is considerably small. Therefore, if dust stuck to the magnetic tape lodges in the gap between the magnetic tape and the magnetic head, then the recording and reproducing characteristics are greatly affected.
On the other head, a video tape cassette operated with a rotary magnetic head system is extensively employed for high-density signal recording. The video tape cassette has a rockable guard panel over the opening formed in the front wall thereof to protect the magnetic tape from damage and to prevent dust from affecting the high-density signal recording and reproducing characteristics.
In more detail, ABS resin or PS resin is most extensively employed to form the above-described magnetic tape cassette. However, when the guard panel is swung back and forth, it slides on the cassette case, forming a powder of the resin. Since the guard panel is swung to open and close the opening formed in the front end wall of the cassette case, the resin powder is produced near the opening. Accordingly, the resin powder thus produced is liable to enter the cassette case through the opening, thus adversely affecting the signal recording and reproduction characteristics of the magnetic tape.
In the rotary magnetic head system, in general, the signal recording and reproducing operations are carried out with the magnetic tape run in one direction. Thus, in the magnetic tape cassette, it is unnecessary that both sides (sides A and B) thereof be symmetrical in structure. Furthermore, in the rotary magnetic head system, in general, two magnetic heads are inclined at certain angles with respect to the tape running direction and alternately contact the magnetic tape while being rotated. This has the effect of sweeping dust away from the magnetic tape. Therefore, the effect of dust on the signal recording and reproducing characteristics is relatively small when compared with that of dust on the characteristic in the fixed magnetic head system.
A magnetic tape cassette to which the technical concept of the invention is applied is one which is operated in the fixed magnetic head system and has two sides (sides A and B) so that the upper and lower halves of the magnetic tape are separately used. In the fixed magnetic head system, as explained above, dust adversely affects the signal recording and reproducing characteristic more than in the case of a rotary magnetic head system. Therefore, the guard panel of the magnetic tape cassette should have a more effective dust-proofing effect than that of the aforementioned video tape cassette.